Method and system adjusting an exhaust heat recovery valve

ABSTRACT

A method for adjusting an exhaust heat recovery valve is presented. In one embodiment, the method may control an amount of boost provided by a turbocharger to an engine.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/068,449, “METHOD AND SYSTEM ADJUSTING AN EXHAUST HEATRECOVERY VALVE,” filed Oct. 31, 2013, which is a divisional of U.S.patent application Ser. No. 12/878,846, “METHOD AND SYSTEM ADJUSTING ANEXHAUST HEAT RECOVERY,” filed on Sep. 9, 2010, now U.S. Pat. No.8,601,811, the entire contents of each of which are hereby incorporatedby reference for all purposes.

FIELD

The present description relates to a method for adjusting an exhaustheat recovery valve. The method and system may be particularly usefulfor a turbocharged engine.

BACKGROUND AND SUMMARY

One way to increase engine efficiency is to reduce engine displacementand boost the engine. By boosting the engine, the engine air capacitycan be increased such that additional fuel may be supplied to the engineto increase engine power output. However, it may be possible for aturbocharger waste-gate to degrade in performance during engineoperation. For example, a waste-gate range of motion may be reducedduring some operating conditions. If the waste-gate does not open as faras is desired, it may be difficult to control turbocharger compressorsurge under some engine operating conditions. Further, the turbochargermay produce more boost than is desired during some engine operatingconditions when the waste-gate range of motion is less than desired.

The inventors herein have recognized the above-mentioned disadvantagesand have developed an engine method, comprising: in response toturbocharger waste-gate degradation, increasing a level of exhaust heatextracted from exhaust gas upstream of a turbocharger turbine to reduceflow through a turbocharger compressor.

By adjusting the position of a heat recovery valve in an exhaust system,it may be possible to control engine boosting and turbochargercompressor surge when a turbocharger waste-gate range of operation isdegraded. In one example, if a turbocharger waste-gate is stuck in aclosed position, a heat recovery valve position is adjusted such that aportion of exhaust gas energy bypasses a turbocharger turbine.Alternatively, if the turbocharger waste-gate opening amount isrestricted to less than its full range of authority, the heat recoveryvalve can be opened in response to a condition where the waste-gateopening becomes limited. For example, if a turbocharger waste-gatefreely opens to 25% if its full opening range, but if the waste-gatefails to open beyond 30% if its full opening range, the heat recoveryvalve may be opened further when the waste-gate position is commanded toa position that is greater than 30% of the waste-gate opening range. Inthis way, it is possible for an exhaust heat recovery valve to assist incontrolling turbocharger boost and surge when operation of aturbocharger waste-gate becomes degraded.

The present description may provide several advantages. In particular,the approach provides an alternative or additional way to control engineboost and turbocharger compressor surge. In addition, the engine systemmay not have to reduce engine output as much as when a heat recoveryvalve is not available to control boost and compressor surge. Furtherstill, in some examples, the heat recovery valve may be used to controlturbocharger operation when the waste-gate is operating as desired butwhere the waste-gate position is not adjustable due to a low level ofboost or due to a low level of actuation force (e.g., low vacuumpressure).

The above advantages and other advantages, and features of the presentdescription will be readily apparent from the following DetailedDescription when taken alone or in connection with the accompanyingdrawings.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages described herein will be more fully understood by readingan example of an embodiment, referred to herein as the DetailedDescription, when taken alone or with reference to the drawings, where:

FIG. 1A is a schematic diagram of one cylinder of an engine;

FIG. 1B is a schematic diagram of a four cylinder engine;

FIG. 2 shows simulated signals of interest when operating an engine;

FIG. 3 shows additional simulated signals of interest when operating anengine;

FIG. 4A is an example flowchart of a method for operating an engine;

FIG. 4B is a continuation of the flowchart shown in FIG. 4A; and

FIG. 5 is an example flowchart of a method for adjusting an exhaust heatrecovery valve.

DETAILED DESCRIPTION

The present description is related to operating an engine. In onenon-limiting example, the engine may be configured as illustrated inFIGS. 1A and 1B. In one example, blow-down gases of a cylinder areseparated from residual cylinder gases and the engine is operatedaccording to the methods of FIGS. 4A-4B providing the signals of FIGS.2-3. Further, if operation of a turbocharger waste-gate or vane positionadjustment degrades, a heat recovery valve is operated according to themethod of FIG. 5 to operate similar to a waste-gate, thereby allowingthe engine boost to be controlled.

Referring to FIG. 1A, a single cylinder of an internal combustion engine10 is shown. Internal combustion engine 10 is comprised of a pluralityof cylinders as shown in FIG. 2. Engine 10 includes combustion chamber30, coolant sleeve 114, and cylinder walls 32 with piston 36 positionedtherein and connected to crankshaft 40. Combustion chamber 30 is showncommunicating with intake manifold 44 and exhaust manifold 80 viarespective intake valves 52 and exhaust valves 54. Each intake andexhaust valve may be operated by an intake cam 51 and an exhaust cam 53.Alternatively, one or more of the intake and exhaust valves may beoperated by an electromechanically controlled valve coil and armatureassembly. The position of intake cam 51 may be determined by intake camsensor 55. The position of exhaust cam 53 may be determined by exhaustcam sensor 57. In one example, exhaust cam 53 includes separate anddifferent cam lobes that provide different valve profiles for each oftwo exhaust valves for combustion chamber 30. For example, a first camprofile of a first exhaust valve of combustion chamber 30 has a firstlift amount and a first opening duration. A second cam profile of asecond exhaust valve of combustion chamber 30 has a second lift amountand a second opening duration, the first lift amount less than thesecond lift amount and the first opening duration less than the secondlift duration. In addition, in some examples, the phase of the first andsecond cam profiles may be individually adjusted relative to the phaseof the engine crankshaft. Thus, the first cam profile can be positionedto open the exhaust valve BDC of the expansion stroke of combustionchamber 30. In particular, the first cam profile can open and close afirst exhaust valve before BDC expansion stroke. Further, the first camprofile can be adjusted in response to engine speed to adjust exhaustvalve opening and closing to selectively exhaust blow-down gas ofcombustion chamber 30. On the other hand, the second cam profile canopen a second exhaust valve after BDC expansion stroke. Thus, the timingof the first exhaust valve and the second exhaust valve can isolatecylinder blow-down gases from residual gases.

In an example where engine warm-up is not the priority mode, themajority of the initial blow-down energy is directed to the turbine 164.The remainder of expelled exhaust gas emerges at a low pressure and isdirectly routed to the exhaust after treatment 72 bypassing the turbine.The higher pressure exhaust gas is also optionally deployable as EGR orheatant for warming transmission fluid, engine oil, coolant, or engineair via a heat exchanger.

Fuel injector 66 is shown positioned to inject fuel directly intocylinder 30, which is known to those skilled in the art as directinjection. Alternatively, fuel may be injected to an intake port, whichis known to those skilled in the art as port injection. Fuel injector 66delivers liquid fuel in proportion to the pulse width signal. Fuel isdelivered to fuel injector 66 by a fuel system (not shown) including afuel tank, fuel pump, and fuel rail (not shown). Distributorlessignition system 88 provides an ignition spark to combustion chamber 30via spark plug 92

During operation, each cylinder within engine 10 typically undergoes afour stroke cycle: the cycle includes the intake stroke, compressionstroke, expansion stroke, and exhaust stroke. During the intake stroke,generally, the exhaust valve 54 closes and intake valve 52 opens. Air isintroduced into combustion chamber 30 via intake manifold 46, and piston36 moves to the bottom of the cylinder so as to increase the volumewithin combustion chamber 30. The position at which piston 36 is nearthe bottom of the cylinder and at the end of its stroke (e.g. whencombustion chamber 30 is at its largest volume) is typically referred toby those of skill in the art as bottom dead center (BDC). During thecompression stroke, intake valve 52 and exhaust valve 54 are closed.Piston 36 moves toward the cylinder head so as to compress the airwithin combustion chamber 30. The point at which piston 36 is at the endof its stroke and closest to the cylinder head (e.g. when combustionchamber 30 is at its smallest volume) is typically referred to by thoseof skill in the art as top dead center (TDC). In a process hereinafterreferred to as injection, fuel is introduced into the combustionchamber. In a process hereinafter referred to as ignition, the injectedfuel is ignited by known ignition means such as spark plug 92, resultingin combustion. During the expansion stroke, the expanding gases pushpiston 36 back to BDC. Crankshaft 40 converts piston movement into arotational torque of the rotary shaft. Blow-down gases may be releasefrom the cylinder before the cylinder reaches BDC if desired by openingat least one exhaust valve of an exhaust valve pair. Further, during theexhaust stroke, the other exhaust valve of an exhaust valve pair opensto release the residual combusted air-fuel mixture to exhaust manifold80 and the piston returns to TDC. Note that the above is shown merely asan example, and that intake and exhaust valve opening and/or closingtimings may vary, such as to provide positive or negative valve overlap,late intake valve closing, or various other examples.

Referring now to FIG. 1B, a schematic diagram of a four cylinder enginecomprised of cylinders configured with cylinders as shown in FIG. 1A isshown. Engine 10 includes cylinder number one 12 with intake I valvesand exhaust E valves. Likewise, cylinder number two 14, cylinder numberthree 16, and cylinder number four 18 include intake I and exhaust Evalves. Cylinders are supplied air via intake manifold 44. In addition,intake manifold 44 is shown communicating with optional electronicthrottle 62 which adjusts a position of throttle plate 64 to control airflow from intake boost chamber 46. Compressor 162 draws air from airintake 42 to supply intake boost chamber 46. Air may also bypasscompressor 162 via compressor bypass valve 165. Exhaust gases spinturbine 164 which is coupled to compressor 162. In some examples, awaste-gate 151 allows exhaust gases to bypass turbine 164. A highpressure, dual stage, fuel system may be used to generate fuel pressuresat injectors 66.

Distributorless ignition system 88 provides an ignition spark tocylinders 12, 14, 16, and 18 via sparks plug 92 in response tocontroller 12. Exhaust from cylinders 12, 14, 16, and 18 is directed toexhaust manifolds 80 and 84 via exhaust runners 82 and 86. Exhaustrunners 82 extend from cylinders 12, 14, 16, and 18 to exhaust manifold80. Exhaust runners 86 extend from cylinders 12, 14, 16, and 18 toexhaust manifold 84. Exhaust runners 82 are isolated from exhaustrunners 86 when at least one exhaust valve of each cylinder is in aclosed position. Accordingly, exhaust from cylinders 12, 14, 16, 18exits to exhaust runners 82 and 86 and only recombines downstream ofvalves 140 or 144 in the direction of exhaust flow. Alternatively, whenexhaust gas recirculation is present by opening exhaust gasrecirculation (EGR) valve 142, exhaust gases may flow to exhaust runners82 and enter intake manifold 44. After entering intake manifold 44,exhaust gases may enter exhaust runners 86 after combustion events incylinders 12, 14, 16, and 18. Thus, exhaust gases may not flow directlybetween exhaust runners 82 and 86.

The Universal Exhaust Gas Oxygen (UEGO) sensor 126 is shown coupled toexhaust manifold 84 upstream of catalysts 70 and 72. Alternatively, atwo-state exhaust gas oxygen sensor may be substituted for UEGO sensor126. Turbocharger turbine 164 receives exhaust gases from exhaustmanifold 80 to power air compressor 162. Exhaust gas heat recoverydevice 146 also receives exhaust gases from exhaust manifold 80. In oneexample, exhaust gas heat recovery device is a gas-to-liquid heatexchanger. In another example, exhaust gas heat recovery device is a gasto gas heat exchanger. In still another example, exhaust gas heatrecovery device 146 may be a Peltier device.

EGR valve 142, heat recovery valve (HRV) 140, and positive turbineshut-off valve 144 control the flow of exhaust gases from exhaustmanifold 80. However, in some examples valve 144 may be omitted. Inother examples, valve 140 and 144 may be configured as a single Yconnection, sometimes referred to as a diverter valve. Exhaust fromexhaust manifold 80 may flow to intake manifold 44 via conduit 158 whenEGR valve 142 is in an open position. Exhaust from exhaust manifold 80may flow to turbine 164 via conduit 150 when turbine shut-off valve 144is in an open position. Exhaust from exhaust manifold 80 may flow toconduit 152 when HRV is in an open position.

Converters 70 and 72 can include multiple catalyst bricks, in oneexample. In another example, multiple emission control devices, eachwith multiple bricks, can be used. Converters 70 and 72 can be athree-way type catalyst in one example.

Controller 12 is shown in FIG. 1 as a conventional microcomputerincluding: microprocessor unit 102, input/output ports 104, read-onlymemory 106, random access memory 108, keep alive memory 110, and aconventional data bus. Controller 20 is shown receiving various signalsfrom sensors coupled to engine 10, in addition to those signalspreviously discussed, including: engine coolant temperature (ECT) from atemperature sensor (not shown); a position sensor 134 coupled to anaccelerator pedal 130 for sensing force/deflection applied by foot 132;a measurement of engine manifold absolute pressure (MAP) from pressuresensor 122 coupled to intake manifold 44; a measurement of boostpressure from pressure sensor 123; a measurement of air mass enteringthe engine from sensor 120; and a measurement of throttle position froma sensor (not shown). Barometric pressure may also be sensed (sensor notshown) for processing by controller 12. In a preferred aspect of thepresent description, an engine position sensor (not shown) produces apredetermined number of equally spaced pulses every revolution of thecrankshaft from which engine speed (RPM) can be determined.

In some examples, the engine may be coupled to an electric motor/batterysystem in a hybrid vehicle. The hybrid vehicle may have a parallelconfiguration, series configuration, or variation or combinationsthereof. Further, in some embodiments, other engine configurations maybe employed, for example a diesel engine.

Thus, the system of FIGS. 1A and 1B provides for an engine system,comprising: a first exhaust conduit extending from a first exhaust portof a cylinder; a second exhaust conduit extending from a second exhaustport of the cylinder, the second exhaust port isolated from the firstexhaust port by a heat recovery valve and a turbine; a heat exchangerlocated in a first branch of the first exhaust conduit, an outlet of theheat exchanger directed to an intake manifold and the second exhaustconduit; a turbocharger located in a second branch of the first exhaustconduit; a first catalyst and a second catalyst located along the secondexhaust conduit; and a controller, the controller including instructionsfor adjusting a position of the heat recovery device in response to aboost amount during a condition of degradation of a waste-gate of theturbocharger. The engine system includes where the controller includesfurther instructions for adjusting a boost limit in response to the heatrecovery valve being stuck in at least a partially open position. Theengine system includes where the controller includes furtherinstructions for increasing an amount of spark retard in response to theheat recovery valve being stuck in a closed position during a coldengine start. The engine system includes where the controller includesfurther instructions for adjusting a position of the heat recovery valvein response to barometric pressure. The engine system includes where thecontroller includes further instructions for adjusting the position ofthe heat recovery valve in response to a flow rate.

Further, FIGS. 1A and 1B provide for an arrangement where exhaust gasesare split into a higher pressure conduit and a lower pressure conduit.The gases in the higher pressure conduit may be selectively routedthrough an EGR cooler and into the engine air intake via a heat recoverydevice. Further, the higher pressure exhaust gases can be routed throughthe heat recovery device to the low pressure exhaust gas path. Furtherstill, the higher pressure exhaust gases can be routed through aturbocharger turbine and into the low pressure exhaust path. In someexamples, the EGR cooler and the heat recovery device are the samedevice.

Referring now to FIGS. 2 and 3, simulated signals of interest whenoperating an engine are shown. For each plot shown in FIGS. 2 and 3,time begins at the right side of the plot and increases to the left.

The first plot from the top of FIG. 2 represents desired engine torque.Desired engine torque may be determined from an operator's depression ofa pedal or from a signal of a system (e.g., a hybrid vehiclecontroller). The second plot from the top of FIG. 2 represents enginespeed. The third plot from the top of FIG. 2 represents enginetemperature. The horizontal dotted line 202 in the engine temperatureplot represents a threshold engine temperature. The fourth plot from thetop of FIG. 2 represents desired engine boost. The fifth plot from thetop of FIG. 2 represents the position of a turbine shut-off valve (TSV).The TSV is open when the illustrated signal is at a higher level. TheTSV is closed when the illustrated signal is at a lower level. The TSVmay completely or partially limit exhaust flow through the turbine. Thefirst, second, and third plots from the top of FIG. 3 are the same asthe first three plots from the top of FIG. 2. The plots are repeated toimprove the viewer's identification of selected operating conditions.The fourth plot from the top of FIG. 3 represents the position of theexhaust heat recovery valve (HRV). The HRV is open when the illustratedsignal is at a higher level. The HRV is closed when the illustratedsignal is at a lower level. The fifth plot from the top of FIG. 3represents the position an EGR valve. The verticals markers near T₁-T₅are provided to show timing of events of interest.

At time T₀, the engine is started from cold operating conditions. Noticethat engine temperature is near the bottom of the engine temperatureplot so as to indicate a cooler engine temperature. As time increases tothe right, engine temperature increases as the engine warms up. Thedesired engine torque is also at a low level indicating that theoperator or other system is not requesting much engine torque (e.g.,when the engine is idling). Accordingly, the desired engine boost isalso low at T₀. The turbine shut-off valve is in a low state at T₀indicating that the valve is in a closed position. By closing theturbine shut-off valve, more exhaust heat may be directed to the exhaustgas heat recovery device. Similarly, the EGR valve position signal is ata low level indicating that the EGR valve is closed. At colder enginetemperatures and after an engine start, an engine may have lesstolerance for EGR. Thus, the EGR valve is closed in this example. On theother hand, the HRV is set to an open position to allow exhaust gases totransfer energy to the exhaust heat recovery device during the enginestart so that energy from the exhaust can be transferred to enginecoolant, engine oil, transmission oil or other areas that may exhibithigher friction at lower temperatures. Further, returning exhaust heatto the engine when the engine is cold can reduce particulate emissions.Therefore, in one example, the HRV valve can be controlled to returnexhaust heat to the engine until a threshold temperature at whichparticulate emissions for a specified engine load are less than athreshold level.

At time T₁, the desired engine torque signal begins to transition to ahigher level indicating an increase in desired engine torque. Atsubstantially the same time, the engine speed begins to increase. Theengine speed and desired engine torque continue to increase until alevel of desired torque is reached. When the desired boost reaches alevel where it is desirable to start powering up the turbocharger, theturbine shut-off valve is opened to activate the turbocharger.Consequently, the TSV opens at T₂ as indicated by the TSV signaltransitioning from a low level signal to a high level signal. Atsubstantially the same time, the HRV begins to close so that additionalamounts of exhaust gas can be directed to the turbocharger turbine.Between time T₂ and time T₃, the HRV continues to close as desiredengine torque, desired boost, and engine speed increase. In addition,engine temperature continues to increase and the EGR valve is opened asindicated by the EGR valve position signal increasing.

At time T₃, the desired engine torque falls as do desired boost andengine speed. Desired engine torque may decrease in response an operatortipping out (e.g., at least partially releasing) of a throttle or apedal. In response to less desired torque, the EGR valve position closesand the HRV opens. When the desired level of torque is low, the engineneeds less air to provide a desired level of torque. As a result, theengine may be able to tolerate less EGR. Consequently, additionalexhaust may be directed to the exhaust heat recovery device since theengine requires less exhaust gas. Between times T₃ and T₄, the engine isoperated at a low load (e.g., during a deceleration).

At time T₄, the engine load begins to increase as do desired boostpressure, engine speed, and engine speed. Consequently, more exhaustenergy is required to meet the boost demand so the HRV begins to close,thereby increasing the exhaust energy supplied to the turbine.

At time T₅, the engine reaches a threshold temperature as indicated byhorizontal dotted line 202. In one example, the engine is at operatingtemperature when it reaches the temperature indicated by horizontal line202. Consequently, exhaust heat is no longer supplied to the engine ortransmission as indicated by the HRV substantially closing at T₅. TheEGR valve position indicates that the EGR valve is opened between T₄ andT₅. Thus, exhaust may be directed to the intake manifold and to theturbine after time T₄. The method described in FIGS. 4A and 4B iscapable of operating according to the plots of FIGS. 2 and 3.

In a system such as shown in FIGS. 1A and 1B, high pressure exhaust ismanaged in three paths. The first path is cooled EGR via the EGR valve.The second path is heat recovery through the heat recovery device. Thethird is controlling boost. In one example, during a performance modepriority of high pressure exhaust gases is given to supplying theturbocharger turbine. When EGR is used primarily for emissions control,cool EGR has priority over the turbine and so exhaust gases are routedto the heat recovery device and the intake manifold. When no cooled EGRis required exhaust gases are routed to the heat recovery device and theturbine.

Referring now to FIG. 4A, an example flowchart of a method for operatingan engine is shown. The numerical identifiers used in the description ofFIG. 4 are based on the system of FIG. 1A. The method may be executed bythe controller of FIG. 1B.

This method prioritizes engine torque when demanded by the vehicleoperator. When the operator desired torque level is satisfied by enginetorque output, warm-up is prioritized by directing the path of exhaustgases. Warm-up control of exhaust gases ceases when a threshold enginetemperature is reached. EGR control continues after the engine is warmedup.

At 402, engine operating conditions are determined. Engine operatingconditions may include but are not limited to a temperature of theengine, atmospheric temperature and pressure, engine speed, engine load,time since engine start, number of combustion events since the enginewas last stopped, intake manifold pressure, desired engine torque,engine load, boost pressure, and throttle position. Method 400 proceedsto 404 after engine operating conditions are determined.

At 404, method 400 judges whether or not engine temperature is less thana threshold temperature. For example, if engine temperature is less thana threshold temperature of 20 degrees C., method 400 proceeds to 406.Otherwise, method 400 proceeds to 418.

At 406, method 400 judges if EGR is desired. In one example, EGR isdesired during predetermined engine operating conditions. For example,when engine coolant temperature is greater than a threshold temperature,when engine load is greater than a first threshold engine load and lessthan a second threshold engine load, and when engine speed is greaterthan a first threshold engine speed and less than a second thresholdengine speed. If method 400 judges that EGR is desired, method 400proceeds to 422 of FIG. 4B. Otherwise, method 400 proceeds to 408.

At 408, method 400 judges if boost is desired. In one example, an amountof boost provided by a compressor such as a turbocharger may bedetermined in response to an operator engine torque demand from a pedalsensor or other device. In another example, an amount of boost may bedetermined in response to a hybrid controller. If boost is desired,method 400 proceeds to 410. Otherwise, method 400 proceeds to 414.

At 410, method 400 judges whether or not desired boost is greater than athreshold amount. In one example, the threshold amount of boost isrelated to a higher level of desired torque so that substantially fullengine power is available to the operator. In another example, thethreshold amount of boost may be related to an engine temperature oranother engine operating condition. If the desired boost is greater thana threshold amount, method 400 proceeds to 412. Otherwise, method 400proceeds to 416.

At 412, method closes a heat recovery valve, opens a turbine shut-offvalve, closes an EGR valve, and adjusts the turbocharger to provide thedesired level of boost. By closing the heat recovery valve at 412 andEGR valve 142, substantially all exhaust energy in exhaust manifold 80can be directed to turbine 164. As such, engine power output may beincreased by allowing compressor 162 to provide higher levels of boostto the engine. In one example, the turbine waste-gate or vane positioncan be adjusted in response to a difference between a desired boostpressure and an observed or measured boost pressure. The desired boostpressure can be determined from empirically determined boost values thatare indexed by engine speed and desired engine torque.

In one example at 412, the cam phase of exhaust valves that control flowinto exhaust runners 82 can be adjusted to vary timing of when blow-downgases are released to exhaust runners 82 from cylinders 12, 14, 16, and18. In particular, at lower engine speeds exhaust timing of valves thatcontrol exhaust flow to exhaust runners 82 can be such that the exhaustvalve opens relatively late and closes substantially at BDC expansionstroke of the cylinder. At higher engine speeds exhaust timing of valvesthat control exhaust flow to exhaust runners 82 can be such that theexhaust valve opens relatively early and closes before BDC expansionstoke of the cylinder. Thus, the timing of the exhaust valves thatcontrol exhaust flow to exhaust runners 82 is retarded at lower enginespeeds.

The timing of exhaust valves that control flow from cylinders 12, 14,16, and 18 to exhaust runners 86 can also be adjusted at 412. Inparticular, valves controlling exhaust gas flow to exhaust runners 86are also retarded at lower engine speeds. In particular, valvescontrolling exhaust gas flow to exhaust runners 86 are opened atsubstantially BDC exhaust stroke at lower engine speeds. At higherengine speeds, valves controlling exhaust gas flow to exhaust runners 86are opened before BDC exhaust stroke. Thus, the exhaust valves thatcontrol exhaust gas flow to exhaust runners 82 control the flow ofblow-down gases from cylinders 12, 14, 16, and 18 to exhaust manifold80. And, the exhaust valves that control exhaust gas flow to exhaustrunners 84 control the flow of residual gases from cylinders 12, 14, 16,and 18 to engine exhaust manifold 84. By separating the blow-down gasfrom the residual gas, exhaust gases with higher energy can be directedto the turbine and the exhaust heat recovery device.

At 416, method 400 at least partially opens the heat recovery valve,closes the EGR valve, opens the turbine shut-off valve, and adjusts theturbocharger. Thus, at 416 it is desirable to provide boost and recoverheat energy from the exhaust. Heat energy from the exhaust may be usedto more quickly warm the engine by transferring the heat energy to theengine coolant. Further, the exhaust heat energy may be used to heat thetransmission. In these ways, the exhaust gas may be used to reduceengine friction during a cold start.

In one example, the HRV (e.g., 140 of FIG. 1B) can be adjusted tooperate similar to a turbocharger waste-gate so that exhaust gas energythat is not needed to provide a desired level of boost is provided tothe exhaust heat recovery device. For example, if the turbine isproviding or capable of providing a desired level of boost with lessthan the amount of exhaust gas provided by the engine via exhaustmanifold 80, then the exhaust gas heat recovery valve 140 can be atleast partially opened to allow flow through the exhaust heat recoverydevice 146. When the exhaust heat recovery valve acts as a turbinebypass for a portion of exhaust gases traveling through exhaust manifold80, the waste-gate or vanes of turbine 164 can be set such that theturbine is operating at substantially its highest efficiency given theexhaust flow to the turbine. For example, the turbine waste-gate can beclosed or the vanes can be set at a highly efficient position. Further,if the engine is operating at cold start conditions, the turbineshut-off valve may be closed until the engine reaches a desired enginespeed or temperature so that substantially all the exhaust heat isrecovered by the exhaust heat recovery device 146.

In another example, the HRV is adjusted so that a proportion of theexhaust energy is directed to the exhaust heat recovery device. Forexample, the HRV position can be adjusted in response to engine load ordesire engine torque so that a portion of exhaust energy is directed toheat recovery device 146 while the remainder of the exhaust gas energyis directed to the turbine 164. Of course, the percentage of exhaustgases directed to the heat recovery device can be varied depending onengine operating conditions. For example, if the engine is cold thepercentage of exhaust gases directed to the exhaust gas heat recoverydevice can be higher than the percentage of exhaust gases directed tothe turbine. Under substantially the same engine operating conditions,but at a higher engine temperature, the percentage of exhaust gasesdirected to the turbine can be greater than the percentage of exhaustgases directed to the exhaust gas heat recovery device.

At 414, method 400 closes the EGR valve, opens the HRV, and closes theEGR valve. Since EGR and boost are not required at 414, substantiallyall exhaust energy in exhaust manifold 80 can be directed to the exhaustgas heat recovery device 146. This mode of operation may be particularlyuseful during engine starting because a higher amount of exhaust gasenergy can be recovered by the exhaust gas heat recovery device.

At 422, method 400 judges whether or not boost is desired. In oneexample, an amount of boost is determined as described at 408. Inparticular, boost may be determined in response to an operator enginetorque demand from a pedal sensor or other device or in response to ahybrid controller. If boost is desired, method 400 proceeds to 428.Otherwise, method 400 proceeds to 424.

At 428, method 400 opens the EGR valve, opens the HRV valve, and opensthe turbine shut-off valve. Thus, method 400 can provide EGR, turbinepower, and recovered exhaust heat at least under some conditions. In oneexample, priority can be assigned to EGR, boost, and exhaust heatrecovery during different operating conditions. For example, an amountof exhaust energy used to provide boost can be given higher priority ascompared to exhaust for EGR and the amount of exhaust for EGR can begiven priority over the amount of exhaust provided to the exhaust gasheat recovery device. Thus, if the amount of exhaust heat energyprovided by the engine to exhaust manifold is insufficient to operatethe turbine, the EGR valve, and the exhaust heat recovery device undersome engine operating conditions, the available exhaust energy can bedirected to areas with higher priority by at least partially closingeither the EGR valve, the HRV, or the turbine shut-off valve. In oneexample, the amount of available exhaust energy can be determined basedon engine load and exhaust valve timing.

In one example, a desired pressure in exhaust manifold 80 is establishedin response to engine operating conditions (e.g., engine speed anddesired engine torque). Further, the EGR valve position is adjusted inresponse to a desired EGR flow rate and a pressure differential betweenexhaust manifold 80 and intake manifold. The HRV valve position isvaried to maintain the desired exhaust pressure in exhaust manifold 80.During conditions where the desired pressure of manifold 80 cannot bemaintained by adjusting the HRV, the HRV may be closed.

At 424, method 400 closes the turbine shut-off valve. By closing theturbine shut-off valve, additional exhaust gases can be directed to EGRand heat recovery. Method 400 proceeds to 426 after the turbine shut-offis shut off.

At 426, method 400 adjusts the EGR valve and the HRV proportionally toprovide EGR and recovered exhaust heat. In particular, the EGR valve isadjusted to provide the desired EGR flow rate by adjusting the positionof the EGR valve in response to a desired EGR flow rate and the pressuredifferential between the exhaust manifold 80 and the intake manifold 44.The HRV is adjusted to provide a desired level of pressure in exhaustmanifold 80. The desired level of pressure in the exhaust manifold isdetermined in response to engine speed and desired torque. Thus, the HRVis adjusted in response to engine speed and desired torque to provide adesired level of pressure in exhaust manifold 80.

At 418, method 400 opens the turbine shut-off valve, closes the HRV. TheHRV valve is closed to increase the level of exhaust energy supplied tothe EGR valve and the turbine. In this way, the output of the turbinemay be increased. Method 400 proceeds to 420 after the turbine shut-offvalve is opened and after the HRV is closed.

At 420, method 400 adjusts the EGR valve position and the turbocharger.The EGR valve position is adjusted based on a desired EGR rate and thepressure differential between the intake manifold 44 and the exhaustmanifold 80. The turbine waste-gate is adjusted according to desiredboost pressure and compressor speed. In one example, the waste-gate isopened when compressor speed exceeds a threshold. Further, thewaste-gate is opened in response to boost pressure exceeding a desiredboost pressure.

Referring now to FIG. 5, a method for adjusting an exhaust gas heatrecovery valve is shown. The method may be executed by the controller ofFIG. 1B. Further, although the method of FIG. 5 explicitly mentionsdegradation of waste-gate operation, the method of FIG. 5 also appliesto turbochargers having adjustable vanes.

At 502, method 500 determines engine operating conditions. Engineoperating conditions may include but are not limited to a temperature ofthe engine, atmospheric temperature and pressure, engine speed, engineload, time since engine start, number of combustion events since theengine was last stopped, intake manifold pressure, desired enginetorque, engine load, boost pressure, exhaust pressure, HRV position,waste-gate position, and throttle position. Method 500 proceeds to 504after engine operating conditions are determined.

At 504, method 500 judges whether or not the HRV is operational. In oneexample, the HRV may be judged operational if it responds in an expectedway to opening and closing commands issued by a controller. For example,if the HRV is commanded open and the HRV responds as desired, exhaustgases will flow through the heat recovery device and increasetemperatures in the exhaust passage downstream of the heat recoverydevice. If a temperature sensor responds to the open HRV it may bejudged that the HRV is operational. If it is judged that the HRV isoperational, method 500 proceeds to 504. Otherwise, method 500 proceedsto 514.

At 506, method 500 judges whether or not turbocharger waste-gateoperation is degraded. In one example, operation of a waste-gate may bedetermined to be degraded if boost pressure does not respond to acommand for opening and closing a waste-gate. In another example,operation of a waste-gate may be determined to be degraded if a sensedposition of a waste-gate does not respond a command for opening andclosing a waste-gate. Method 500 proceeds to 508 if it is judged thatoperation of a waste-gate is degraded. Otherwise, method 500 proceeds toexit.

At 508, method 500 judges whether or not waste-gate opening is less thandesired. In one example, it may be judged that the turbochargerwaste-gate is opening less than desired if a boost pressure is higherthan is desired. In another example, it may be judged that theturbocharger waste-gate is opening less than desired if the compressorspeed or the turbine speed is greater than is desired. If it is judgedthat the waste-gate is opening less than is desired, method 500 proceedsto 510. Otherwise, method 500 proceeds to exit.

At 510, method 500 determines flow through the turbocharger waste-gate.In one example, the flow through the turbocharger waste-gate isdetermined from the position of the waste-gate and the flow through theengine. In another example, the flow through the turbocharger waste-gatemay be inferred from boost pressure and the flow through the engine. Inparticular, an empirically determined table indexed by engine air flowand boost pressure outputs an amount of flow through the waste-gate. Inan alternative, example, rather than determining flow through thewaste-gate, method 500 may skip 510 and adjust the HRV via a controllerin response to boost pressure. Method 500 proceeds to 512 afterdetermining flow through the waste-gate.

At 512, method 500 adjusts the HRV. In one example, the flow through thewaste-gate determined at 510 is subtracted from a desired waste-gateflow. The desired waste-gate flow may be empirically determined andstored in a table that is indexed based on engine speed and desiredload. The waste-gate flow determined at 510 is subtracted from thedesired waste-gate flow providing a waste-gate remainder flow. The HRVis then positioned to provide the waste-gate remainder flow so thatsubstantially the same amount of exhaust gas bypasses the turbine aswhen the waste-gate is not operating in a degraded state. Further, theposition of the HRV can be adjusted in response to boost pressure. Forexample, the actual boost pressure may be subtracted from the desiredboost pressure, thereby providing a boost pressure error signal. Theboost pressure error signal can by multiplied by a gain and then appliedto the HRV command signal. Further, the position of the HRV can beadjusted to compensate for barometric pressure. For example, the gainapplied to the HRV command may be varied based on barometric pressure.In this way, the HRV can be positioned to regulate the amount of exhaustflowing to the turbine.

In another example, the HRV can be adjusted by a controller (e.g., aproportional/integral controller) in response to a difference between adesired boost pressure and a measured boost pressure. For example, whenthe measured boost pressure is greater than the desired boost pressure,the opening of the HRV can be proportionally increased. Further, the HRVcan be further closed in response to an integrated error between thedesired boost pressure and the actual boost pressure. Method 500proceeds to exit after adjusting the HRV position.

At 514, method 500 judges whether or not the HRV is held open. In oneexample, the position of the HRV may be determined from a positionsensor. In another example, the position of the HRV may be determinedfrom an exhaust gas temperature sensor. Method 500 proceeds to 516 if itis judged that the HRV is held open. Otherwise, method 500 proceeds to520.

At 516, method 500 adjusts an engine boost limit. Since the HRV is heldat least partially open, it may be difficult to achieve as high of aboost pressure as is desired. Therefore, in one example, the boostpressure may be limited to an amount that is based on the position ofthe HRV. If the HRV is opened by a first amount, the boost pressure islimited to a first boost pressure. If the HRV is opened to a secondamount, the second amount greater than the first amount, the boostpressure limit may be lowered to a second boost pressure less than thefirst boost pressure.

In addition to adjusting a boost pressure limit, method 500 may alsoadjust spark advance timing limits, throttle position, and cam timing inresponse to the HRV opening to a position that is greater than isdesired. For example, if the position of the HRV is limiting a boostamount, a command to open a throttle may be increased so that a throttleopening amount is increased as compared to when engine boost is at adesired level. Further, spark timing may be advanced as compared to whenengine boost is at a desired level. Method 500 proceeds to 518 after theboost limit is adjusted.

At 518, method 500 adjusts coolant flow. In one example, if the enginereaches operating temperature and the HRV valve is opened so thatexhaust heat can be transferred to engine oil or transmission oil,method 500 increases a coolant flow rate to the engine and transmission.By increasing the coolant flow to the engine and transmission it may bepossible to control engine and transmission temperature even thoughexhaust energy is transferred to the engine and transmission. In oneexample, the coolant flow to the engine and transmission may beincreased proportionately to the amount of heat transferred to the heatrecovery device. Method 500 proceeds to exit after coolant flow isadjusted.

At 520, method 500 judges whether or not the engine is operating undercold start conditions. In one example, cold start conditions may bedetermined from engine coolant temperature and time or number ofcombustion events from engine start. If it is judged that the engine isoperating in cold start conditions, method 500 proceeds to 522.Otherwise, method 500 proceeds to exit.

At 522, method 522 increases spark retard to increase the exhaust aftertreatment warm up rate. By increasing spark retard, additionalcombustion heat may be directed to the after treatment system so thathydrocarbons produced by the engine may be converted earlier in timefrom the engine start. In this way, the engine exhaust after treatmentsystem temperature may be increased at a higher rate so as to compensatefor less heat being transferred from the exhaust to the engine. Method500 proceeds to exit after spark retard is increased.

Thus, the method of FIGS. 4A, 4B, and 5 provide for an engine method,comprising: in response to turbocharger waste-gate degradation,increasing a level of exhaust heat extracted from exhaust gas upstreamof a turbocharger turbine to reduce flow through a turbochargercompressor. The engine includes where the exhaust heat is extracted byadjusting a position of a heat recovery valve, the heat recovery valvepositioned in an exhaust path of an engine. The engine also includeswhere the heat recovery valve is at least partially opened and whereexhaust flow is diverted from upstream of a turbocharger to an exhaustheat recovery device. The engine method includes where the position ofthe heat recovery valve is adjusted in response to a pressure ratio of aturbocharger compressor. The engine method includes where the positionof the heat recovery valve is further adjusted in response to a flowrate. The engine method includes where closing the turbine shut offvalve reduces turbine output when the waste-gate has reduced capacity tolimit turbine speed. The engine method includes where an amount ofcoolant flow to the engine is increased during a condition ofdegradation of a turbocharger waste-gate. The engine method includeswhere an amount of coolant flow to a transmission is increased during acondition of degradation of the turbocharger waste-gate.

The methods of FIGS. 4A, 4B, and 5 also provide for an engine method,comprising: during a first condition, absent degraded operation of aturbocharger waste-gate, adjusting a position of a heat recovery valvein response to at least one of an engine speed, engine load, and boostpressure, the heat recovery valve providing a variable amount of exhaustgas heat to an exhaust heat recovery device, the variable amount ofexhaust gas heat related to a position of the heat recovery valve; andduring a second condition, including degradation of a turbochargerwaste-gate, adjusting a position of the heat recovery valve to limitflow through a turbocharger compressor. The engine method includes wherea portion of exhaust gas energy is directed to a heat recovery deviceduring the first condition. The engine method includes where theposition of the heat recovery valve is adjusted to provide a desiredexhaust pressure. The engine method includes where the heat recoveryvalve is at least partially opened to limit flow through theturbocharger compressor during the second condition. The engine methodincludes where the position of the heat recovery valve is furtheradjusted in response to a pressure ratio of the turbocharger compressor.The engine method includes where during the first condition a higherportion of exhaust gas is directed to the heat recovery device ascompared to a turbocharger turbine during an engine start where atemperature of an engine is less than a predetermined amount. The enginemethod further comprises increasing a flow of exhaust gases to the heatrecovery device when an operator desired torque level is satisfiedduring the first condition.

As will be appreciated by one of ordinary skill in the art, methodsdescribed in FIGS. 4A-4B and 5 may represent one or more of any numberof processing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various steps orfunctions illustrated may be performed in the sequence illustrated, inparallel, or in some cases omitted. Likewise, the order of processing isnot necessarily required to achieve the objects, features, andadvantages described herein, but is provided for ease of illustrationand description. Although not explicitly illustrated, one of ordinaryskill in the art will recognize that one or more of the illustratedsteps or functions may be repeatedly performed depending on theparticular strategy being used.

This concludes the description. The reading of it by those skilled inthe art would bring to mind many alterations and modifications withoutdeparting from the spirit and the scope of the description. For example,I3, I4, I5, V6, V8, V10, and V12 engines operating in natural gas,gasoline, diesel, or alternative fuel configurations could use thepresent description to advantage.

The invention claimed is:
 1. An engine method, comprising: duringconditions when a turbocharger waste-gate position is not adjustable,increasing a level of exhaust heat extracted from combusted exhaust gasupstream of a turbocharger turbine by adjusting a position of a heatrecovery valve and then flowing the combusted exhaust gas whose heat wasextracted through the heat recovery valve and to an exhaust downstreamof all cylinders, bypassing the turbocharger's turbine to reduce flowthrough a turbocharger's compressor.
 2. The method of claim 1, whereinthe turbocharger waste-gate is not degraded.
 3. The method of claim 2,wherein the waste-gate position is not adjustable due to one of a lowlevel of boost and a low level of vacuum actuation force.
 4. The enginemethod of claim 3, where the heat recovery valve is positioned in anexhaust path of an engine, the method further comprising closing an EGRvalve while increasing the heat extracted.
 5. The method of claim 4,where the heat recovery valve is at least partially opened and whereexhaust flow is diverted from upstream of the turbocharger to an exhaustheat recovery device.
 6. The method of claim 4, where the position ofthe heat recovery valve is adjusted in response to a pressure ratio ofthe turbocharger compressor.
 7. The method of claim 6, where theposition of the heat recovery valve is further adjusted in response to aflow rate.
 8. The method of claim 7, where closing a turbine shut offvalve reduces turbine output when the waste-gate has reduced capacity tolimit turbine speed.
 9. The method of claim 3, where an amount ofcoolant flow to an engine is increased during the conditions when theturbocharger waste-gate position is not adjustable.
 10. The method ofclaim 3, where an amount of coolant flow to a transmission is increasedduring the conditions when the turbocharger waste-gate position is notadjustable.
 11. An engine system, comprising: a first exhaust conduitextending from a first exhaust port of a cylinder; a second exhaustconduit extending from a second exhaust port of the cylinder, the secondexhaust port isolated from the first exhaust port by a heat recoveryvalve and a turbine; a heat exchanger located in a first branch of thefirst exhaust conduit, an outlet of the heat exchanger directed to anintake manifold and the second exhaust conduit; a turbocharger locatedin a second branch of the first exhaust conduit; an EGR valve locateddownstream of the outlet of the heat exchanger and upstream of theintake manifold in the first branch of the first exhaust conduit; afirst catalyst and a second catalyst located along the second exhaustconduit; and a controller including computer-readable instructionsstored on non-transitory memory for: during an engine cold-start whenthe heat recovery valve is not stuck closed, closing the EGR valve whileopening the heat recovery valve to expedite engine heating; and duringan engine cold-start when the heat recovery valve is stuck closed,increasing an amount of spark retard while holding the EGR valve closed.12. The system of claim 11, wherein the controller includes furthercomputer-readable instructions stored on non-transitory memory for: whenthe heat recovery valve is not stuck closed, adjusting a position of theheat recovery valve in response to a boost amount in response to aposition of a waste-gate of the turbocharger not being adjustable. 13.The system of claim 12, wherein the position of the waste-gate is notadjustable due to low waste-gate actuation force.
 14. The system ofclaim 12, wherein the position of the waste-gate is not adjustable dueto low boost pressure.
 15. The system of claim 12, wherein thewaste-gate is not degraded.